Here's something to think about for fun: We've already seen Super Smash Bros. Brawl come and go with no appearance from Mega Man, and PlayStation All-Stars Battle Royale doesn't seem to have anyone from the world of the Blue Bomber, either (maybe next time). Meanwhile, SEGA has released SEGA Superstars Tennis and Sonic & SEGA All-Stars Racing, with the latter getting a sequel coming next month.
It seems that the next logical step would be to create their own game in the "Smash" mold, and why not include Mega Man while they're at it? Hence this concept by Maximiliano and Leonardo, twins from Chile: "Sonic & SEGA All-Stars Warzone:"

At first we thought this was going to be a fan game (and we sort of wish it was), but as it stands, it's basically just some fun fan art. It's a neat concept and they put a lot of work into this idea, so we thought it would be fun to share. And if such a game did come to pass, why not include Mega Man? He is teaming up with Sonic in Archie Comics' "Worlds Collide" storyline next year, after all.